1. Field of the Invention
This invention relates to extruded sheets and, more particularly, to an apparatus for continuously forming a sheet product using cooperating rolls to which a flowable material is continuously supplied.
2. Background Art
Extruded sheets are formed from many different materials, with many different thicknesses, and with different layer constructions. An extruded sheet may be formed by itself or combined with one or more other sheet layers that are concurrently formed or combined after formation.
Common to the above apparatus is the use of an extruder assembly to deliver flowable material to a nip/lamination location on a roll stack assembly so as to initiate sheet layer formation. As this occurs, a sheet die on the extruder assembly and the roll stack assembly are in close proximity to each other. For different reasons, it may be necessary to provide a working space between the sheet die and the roll stack assembly. These components are ideally capable of being spaced adequately to allow unimpeded access to the rolls on the roll stack assembly, as well as the extruder assembly components, to permit system setup, adjustments, and/or regular maintenance.
Heretofore, the roll stack assembly has been guided for movement relative to a subjacent support therefor using casters on the roll stack assembly that move guidingly within a track. Additionally, the roll stack assembly has been integrated as a unit with both a temperature control system, for rolls on the roll stack assembly, and a central control system through which operation of the overall apparatus is programmed and coordinated. This entire unit is moved relative to the extruder assembly to create the aforementioned access/working space.
The use of casters and tracks has a number of inherent drawbacks, which are complicated by the system design wherein the roll stack assembly, temperature control system, and central control system are required to be moved together as a unit.
First of all, the initial setting up of the system using casters and tracks is relatively expensive. Typically, there will be at least four elongate components that must be leveled on a subjacent support surface. Commonly, support surfaces/flooring in facilities wherein this type of equipment is utilized are made with poured concrete that may have many variations attributable either to the initial installation or events occurring thereafter, such as breakage, shifting, etc. The flooring may have to be locally built up or ground to level each of the floor mounted track components at a constant height. This process is complicated by the fact that most of these elements have an appreciable width and are designed to facially engage a subjacent surface over substantially their entire length.
In the event that there is not a precise leveling of all of the tracks, and any other supporting and guiding components, the roll stack assembly may skew as it is repositioned, potentially resulting in a misalignment of the sheet die and a nip location on the roll stack assembly where flowable material is delivered for sheet formation.
Further, in the event that foreign matter or an object finds its way onto the tracks, the path of the moving roll stack assembly may be altered. This may significantly impair movement of the roll stack assembly and/or account for inconsistent and imprecise alignment between the sheet die and the nip location on the roll stack assembly.
By reason of having to move the temperature control system and central control system together with the roll stack assembly, it becomes necessary to incorporate a drive system that has the capacity to repeatedly move this combined unit back and forth in a predetermined path as the relationship between the roll stack assembly and sheet die is changed. Heretofore, it has been common to use a friction drive for this purpose. However, friction drives generally are not consistently and positively operable, particularly when used to advance heavy equipment. Slippage and potential component failure may result that necessitates repairs that may close down a processing line for a significant period of time.
The inability to precisely and consistently advance the roll stack assembly relative to the sheet die may also result in less than the desired precise alignment between the sheet die and rolls at the nip location where the flowable material is delivered. This could result in a compromised sheet product and potentially time consuming and costly repairs that may shut down not only the affected apparatus, but any equipment in a line that is coordinated therewith.
The industry has continued to contend with the above problems primarily because no viable solutions thereto have been devised.